The present invention relates generally to vacuum-operated sewerage control systems utilizing inlet vacuum valves and more particularly to such a system employing an inlet vacuum valve having a tapered plunger to prevent valve jamming and subsequent air leakage as the vacuum seal is impaired.
An operational vacuum sewerage transport system requires that each sewerage inlet point, typically serving one or more houses, include a vacuum valve and controller assembly, providing for intermittent passage of sewage accumulation into an associated transport pipe network which is continuously under vacuum. Vacuum valves are devices for sealing and unsealing the passage between two parts of an evacuated system.
The general structure and method of operation of this type of vacuum valve is described in U.S. Pat. No. 4,171,853 (Cleaver et al). The inlet vacuum valve and controller assembly of the prior art is typically located in a covered pit several feet below ground level for direct in line connection with the transport sewer pipe. Accordingly, inlet vacuum valves in the prior art are opened in response to receiving a signal from a control unit, thereby allowing accumulated sewage to flow into the vacuum sewerage transport system to a remote collection station for further transport to a treatment facility. These vacuum valves are operationally closed to seal the vacuum system by atmospheric pressure that is permitted to enter the internal upper housing of the vacuum valve, in response to a signal from the associated control unit, thereby allowing an internal spring member located in the upper housing to facilitate closing of the vacuum valve. The prior art construction of vacuum valves focused on a rigid plastic internal plunger located within a centrally disposed valve chamber. The plunger was usually cylindrical in shape and operatively connected to the lower end of a piston driving member having a C-shaped cup.
Generally, small stones, chips, and other solid particulate matter are present in the various connecting pipes comprising the transport apparatus of a vacuum sewerage system. Inasmuch as the vacuum valve was cylindrical in shape and contained a rigid internal cylindrical plunger that fit within the vacuum valve chamber, the physical clearance between the internal cylindrical plunger and the wall of the vacuum valve chamber was sufficiently large so as to permit small stones, chips, solid particulate matter and the like to become lodged between the side wall of the valve chamber and the exterior wall of the cylindrical plunger as the particulate matter was transported within the vacuum system during operation of the system. Upon occasion, this caused the cylindrical plunger to become jammed against the wall of the internal valve chamber while the vacuum valve was being pulled to the open position, thereby damaging and not facilitating Proper closing of the vacuum valve when so required by the associated control unit. This would result in continuous air and fluid leakage through the partially open vacuum valve and improper operation of the valve. In addition, the leaking air and fluid would impair efficient operation of the overall vacuum transport system. To restore operation of the system, maintenance personnel had to identify which of the numerous valves had failed and service each of the valves.
Additionally, it was discovered, under repetitive vacuum cycling, that the rubber seat at the end of the rubber cylindrical plunger, which physically engages the internal valve stop of the wye body conduit pipe when the vacuum valve was in the "closed" position, would tend to be pulled away from the end of the cylindrical plunger as the vacuum valve was opened. This would allow small stones, chips, and other solid particulate matter to become lodged between the rubber seat and the end of the plastic cylindrical plunger. This interfered with proper valve closure causing the vacuum valve to leak when in the "closed" position during operation.
The internal valve stop of the wye body conduit pipe of the prior art vacuum valve apparatus was positioned adjacent and below the rubber seat at the end of the plastic cylindrical plunger and would, upon occasion, leak, thereby permitting undesirable air and fluid leakage into the system. Additionally, because of the tight tolerances required between the internal valve seat of the wye body and the rubber stop at the end of the cylindrical plunger, slight deviations in the angle of machining of the valve seat would cause the cylindrical plunger to incorrectly engage the opposed valve stop of the body. Subsequently, this incorrect seating would become yet another source of leakage of air and fluid from the holding sump into the vacuum main.
Another problem experienced in the use of prior art vacuum valves involved leakage through the seal for the valve operating shaft. This seal is provided between the valve and the piston cup to prevent pressure communication between the piston cup and valve chambers of the valve body. Leakage was found to occur in prior art assemblies. Leakage would permit fluid contamination through the seal assembly and into the control unit for the inlet vacuum valve by way of gradual seepage at points about the outer peripheral edge of an internal diaphragm which acts to separate the valve into upper and lower chambers, thereby damaging the individual control unit over time. To the extent sewage contamination leaked into the vacuum chamber of the vacuum valve, or into the associated control unit, maintenance of the vacuum valve was exacerbated and system reliability was impaired.
A common disadvantage relating to the vacuum valves of the prior art is the labor costs associated with locating, servicing and repairing damaged vacuum valves. Also, when damage does occur to the cylindrical plunger of a prior art vacuum valve, replacement of the total vacuum valve is usually required as the most expedient corrective measure. Should the valve be damaged in such a manner so as to result in the occurence of fluid contamination being able to leak into the vacuum valve, an increase in the expense of routine and proper maintenance for all the parts of the vacuum valves and associated control modules will be increased accordingly.